This invention relates to cleaning silos for storing particulate materials where the storing and delivering capacity of the silo is impeded by cohesive masses of the particles within the silo.
In general, silos are typified by coal silos and coal silos are described in the publication AF-791 "Coal Preparation for Combustion and Conversion" (prepared for Electric Power Research Company, May 1978) as follows:
"Coal storage silos are constructed of either steel or concrete although, in the large sizes, steel structures have not proven as economical as concrete. Small concrete silos are built up of precast staves banded together with wire hoops; large silos are constructed of continuously poured concrete using the slipdown technique.
The dimensions of concrete silos have responded to demands for larger capacities and to developments in the state of the art in construction techniques. Silo heights of two to three times the silo diameter are generally found most economical. Capacity of a 70 ft silo, depending on its height, is 10,000 to 15,000 tons. Its installed cost ranges from $100 to $200/ton of storage capacity, . . . Early designs of concrete silos provided rather simple coal drawdown methods. A system of seven gates works well enough with most clean coals, except for occasional rat-holing, i.e., a narrow withdrawal funnel down through the center line of each gate. At other times, coals may bridge over the gate openings, causing flow to become erratic or to halt completely. Preferred designs incorporate the mass or plug flow principle through the use of multiple hoppers having sides sloping upwards at up to 70 degrees, with inlet openings up to 18 ft in diameter and outlet openings as large as practical or rectangular."